symplast

thumb|300px|The apoplastic and symplastic pathways

The symplast (from Greek sym "together" + plasma "formed or moulded substance") is the continuous, living network of cytoplasm that extends through most plant tissues. Its continuity is established by thousands of plasmodesmata — plasma-membrane-lined nanoscopic tunnels that pierce the cell walls and join the cytosol and endoplasmic reticulum of adjacent cells. Because those channels also open into the phloem sieve elements, the symplast provides both short-range and long-range conduits for water, nutrients, metabolites, proteins and RNAs to move between cells along concentration or pressure gradients. By contrast, the apoplast comprises the porous cell-wall matrix and extracellular spaces through which solutes diffuse outside the plasma membrane.